ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 961 



(2 to 3 per cent.) ; if the fragment of bone thus treated be only a few 

 millimetres thick (rat, guinea-pig), twenty-four to forty-eight hours 

 is sufficient to soften it ; thicker pieces may require decalcification for 

 a week. After washing, sections were then made, and these were 

 mounted in glycerine. I'he osteoblasts are now seen as " true ex- 

 cavations " filled with liquid ; fine prolongations become observable, 

 and the primitive bone-cell is found to have been pushed to the wall 

 of the osteoblast, owing to the development of a liquid between it and 

 the osseous matter, and to have carried its prolongations into the 

 neighbouring canaliculi. When a series of young forms are studied 

 one can see spherical vacuoles developed in the interior of the 

 osteoblast. The author explains that this appearance is not due to 

 the production of a gas by the action of the formic acid, as it 

 is seen when such reagents as picric or chromic acids are used 

 instead. 



Mounting Chick Embryos whole.* — Dr. C. S. Minot recom- 

 mends the following method for embryos under forty hours. The egg 

 is opened in the usual manner in warm • 5 per cent, salt solution, 

 the blastoderm freed from the yolk membrane, then swayed with 

 pincers to and fro in the liquid to remove the superfluous yolk, and 

 then floated out on a glass slide on which it is to remain permanently. 

 It is next treated with several fluids, all of which should be dropped 

 on the centre of the germ disk, so as to spread out the blastoderm 

 evenly by their centrifugal flow. Wash off thoroughly with distilled 

 water. Remove the water as fully as possible by bibulous paper, and 

 allow the specimen to remain fully spread out until the edges are 

 dried. The embryo will then escape distortion during the further 

 treatment. Care must be taken that the embryonic area remains 

 moist. Drop on two drops of a ^ per cent, osmic acid solution : 

 leave standing for two or three minutes until a slight browning is 

 produced, wash off again with distilled water, stain with picro- 

 carmine, which dyes the blastoderm after a variable time, according 

 to the intensity of the osmic acid action. The next step is important, 

 because it stops the further darkening by the osmium, which otherwise 

 injures or ruins the specimen. Pour Miiller's fluid, or • 5 per cent, 

 chromic acid solution, on the slide, and leave it overnight. The next 

 morning the blastoderm is ready for dehydration by alcohol, and 

 mounting in the usual manner in balsam, or better, in three parts 

 pure Canada balsam mixed with one part dammar varnish. 



Embryos mounted in this way make very perfect preparations, 

 surpassing, indeed, those otherwise treated. 



Mounting Echinoderm-larvse. — The following mode of pre- 

 paring and mounting Echinoderm-larvfe has been communicated to 

 Dr. Carpenter f by Mr. Percy Sladen who mounted the slides which 

 attracted much attention on the Scientific Evening of 3rd December, 

 1879 (see Vol. III. (1880) p. 375). " For killing and preserving 

 Echinoderm-zooids I have come to prefer either osmic acid or the 



* Amer. Natural., xv. (1881) pp. 841-2. 



t ' The Microscope and its Revelations,' 6th ed., 1881, pp. 646-7. 

 Ser. 2.— Vol. I. 3 S 



